Processes are known for homogenizing bitumen-based mixtures (referred to hereinafter as bituminous mixtures) with granules of Styrene-Butadiene-Styrene (SBS)-based polymeric material and/or polyolefins in order to produce bituminous blends adapted to manufacture flexible bituminous insulating films applicable in particular in the construction field to perform a protective and/or insulating function.
The above mentioned homogenizing processes are currently carried out by means of homogenizer machines which substantially include: an outer casing, within which there is obtained a granule shredding chamber, a disc-shaped stator, which is stably arranged within the shredding chamber in a position coaxial to a horizontal axis, and a rotor which also has a disc shape and is mounted so as to freely rotate within the shredding chamber facing the stator and is fitted on an electric motor shaft which is adapted to rotate it about the horizontal axis.
Specifically, the rotor and the disc-shaped stator each consist of a round plate and a plurality of blades, which are attached on opposite surfaces of the round plates themselves and radially extend from the horizontal axis towards the outer edge of the plates so as to define radial channels therebetween, each radial channel having a gradually decreasing width towards the outer periphery of the surfaces themselves.
In use, the bituminous material and the polymer granules are subjected to an initial premixing and, subsequently, are fed within the shredding chamber of the homogenizer machine, within which the shredding and the final mixing thereof occur at the same time.
Specifically, during the rotation of the rotor, the bituminous material and the polymer granules are pushed by the action of the centrifugal force through the radial channels between the knives towards the outer periphery of the stator and rotor, thus being subjected to cuts by the knives and to a stretching at the same time, i.e. a reduction of their thickness following the forced passage and thus following the compression to which they are subjected within the radial channels.
In order to ensure an appropriate shredding of the granules and their complete mixing with the bituminous material, in the above mentioned homogenizer machines the rotor must rotate so as to reach very high peripheral speeds thereof, typically in the range between 20-50 m/s.
Laboratory tests have shown that once these speeds have been reached by the rotor, the bitumen-granule agglomerate within the shredding chamber reaches a high temperature that determines an alteration of the chemical-physical characteristics of the polymer granules, thus leading to a deterioration of the bituminous blend.
Furthermore, in order to reach the above mentioned rotation speeds of the rotor in the above described homogenizer machines, there is required a high power electric motor, typically on the order of 140-160 kW, which has an especially high energy consumption, and accordingly high operation costs, as well as considerably affecting the overall cost of the homogenizer machine.